Sphenacodontidae, Marsh, 1878 sensu Benson, 2012

Falconnet, Jocelyn, 2015, The sphenacodontid synapsid Neosaurus cynodus, and related material, from the Permo-Carboniferous of France, Acta Palaeontologica Polonica 60 (1), pp. 169-182 : 172-174

Sphenacodontidae indet. 1

Fig. 3A .

1969 “Mâchoire provenant de Lodève”; Heyler 1969: pl. LII: 7.

2002 “Mâchoire provenant de Lodève”; Garric 2002: pl. I: 7 [cop. Heyler 1969: pl. LII: 7].

2008 “mâchoire de Reptile”, “Mâchoire d’un reptile […] probablement d’un Caséidé”; Heyler 2008: 36, fig. 7.

Material.—MNHN.F.LOD213, partial left tooth-bearing dentary preserved mostly as an impression transferred on resin. Collected in 1963 by Jacques Garric ( Garric 2002) from Locality G9, Saint-Julien, Le Bosc Commune, Hérault Department, Languedoc Region, southern France; β bone breccia, lower Viala Formation, Autunian Group, Lodève Basin; Sakmarian, early Permian. The Viala Formation was dated of 289.3 ± 6.7 Ma using U-Pb radiometric dating ( Schneider et al. 2006), a long interval ranging from the late Asselian to the early Kungurian ( International Commission on Stratigraphy 2013). The abundant typical Autunian macro- and microflora ( Broutin et al. 1992) suggest a Late Gzhelian to Asselian age for the underlying Usclas-Saint-Privat and Tuilières-Loiras formations, by comparison with the Autun ( Broutin et al. 1999) and Donets ( Izart et al. 1998a) basins. These datings are in agreement with the Asselian–Sakmarian age assigned by Gand and Durand (2006) to the Tuilières-Loiras and Viala formations on the presence of their footprint associations I and II.

Description

Dentary.—The dentary is a long, shallow bone, measuring about 9 cm in length, that is exposed in lateral view ( Fig. 3A ). Both extremities are missing, anterior to the level of the first preserved tooth and posterior to the tooth row. The dorsal margin of the dentary is gently curved ventrally, but rises dorsally more abruptly at the level of the first preserved mesial teeth. On its anterior half the ventrolateral margin of the dentary exhibits a weak (though distinct) medial inflection. The entire preserved surface is smooth, with no sutures or sutural scars.

Dentition.—Fourteen teeth are preserved and gaps indicate at least two more. Most teeth are damaged, but those located in the middle of the tooth row are fairly well preserved. The teeth decrease steadily in size distally. The teeth have a rather triangular outline with somewhat bulbous, pointed crowns, but lacking evidence of labial or apical wear. In most teeth, the root is slanted and the crown recurved, so that the apex is mesial to the level of the base. On several teeth the mesial and distal margins are strongly compressed labiolingually, forming sharp, apparently unserrated cutting edges that run from the base to the apex of the crown. These features—slanting, recurvature, compression—are less marked distally. The two distalmost teeth are indeed not slanted but vertical, with a symmetrical crown in which the apex is located at the level of the midline of the tooth. They present faint, unserrated, mesiodistal cutting edges, but there is otherwise no sign of labiolingual compression.

Figures

Fig. 3. Unidentified sphenacodontids. A. Sphenacodontidae indet. 1, left dentary (MNHN.F.LOD213), from Saint-Julien, Sakmarian, in lateral view. B. Sphenacodontidae indet. 2, right dentary (UM 5902), from Le Capitoul, Sakmarian, in medial view. C, D. Sphenacodontidae indet. 3, right dentary (UM 5903), from Saint-Julien, Sakmarian, in lateral (C) and medial (D) views. Photographs (C1, D1), explanatory drawings (C2, D2).